Wheel Test Question

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ZiggyDude
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Wheel Test Question

Post by ZiggyDude » Fri Apr 14, 2017 11:30 am

There is a test that my son and I have been doing for wheels. We would get a perfect smooth surface like a kitchen counter, clean and ready it, then build a small ramp. Maybe lift the high end 1/4".

We would then roll the wheels off and record which went the farthest and straightest. Over time we also started listening for the smoothest sound.

They all veer to the side of the hub - but some consistently go much farther than others. Those are the wheels that we would take for bore buffing. I have not been doing any truing (long story). Our results are that we have dominated in the pack but results in the districts have varied.

This year I was curious and got a set of wheels that were listed as "Lightly machined". They were trued and bore inspected.

I did my roll test with these wheels and they were among the worst of any. I was quite surprised.

I did actually put the wheels on a car and they were as fast as any of my best.

Is the test I mentioned useless?

My thanks in advance for your answers.



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Vitamin K
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Re: Wheel Test Question

Post by Vitamin K » Fri Apr 14, 2017 12:08 pm

I don't know that free-rolling the wheel offers much in the way of useful diagnosis for how the wheel performs on the track.

Remember that for concentricity to matter, you need the wheel's tread to be machined true to the bore. If the outside is perfectly round, but the wheel is off center, it will roll well on its own, but poorly when actually mounted on an axle.

The tests I do when evaluating wheels from a box or tube are to put them on an axle and spin them, and look for wobble or shake (or, hopefully, lack thereof), and to put them on a concentricity guage to test for radial runout, relative to the wheel bore.

Finally, as an aside, when you free-roll a wheel down a hill, the heavier wheel will roll further, because its greater mass allows it to accumulate more momentum coming down the slope. For a Pinewood Derby car, the entire system is fixed at 5oz, so heavier wheels don't benefit you there. Rather they hurt you because more energy is invested in making the wheels turn and less in making the car move. A "lightly machined" wheel is going to be lighter than a stock wheel.



ZiggyDude
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Re: Wheel Test Question

Post by ZiggyDude » Fri Apr 14, 2017 1:58 pm

Thanks for the reply.

That is an interesting point about the weight. And that the outside may have been perfect but we have no idea to how well it is in relation to the bore.

The concentricity gauge is of interest to me.

I had not trusted myself in using home tools to true the wheel. The "Pro" mandrel seemed to allow non-centered mounting. Even a good drill press is not perfectly centered. Some say you can do more damage then good.

So, my little test is not something others do?



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Vitamin K
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Re: Wheel Test Question

Post by Vitamin K » Fri Apr 14, 2017 8:55 pm

ZiggyDude wrote:Thanks for the reply.

That is an interesting point about the weight. And that the outside may have been perfect but we have no idea to how well it is in relation to the bore.

The concentricity gauge is of interest to me.

I had not trusted myself in using home tools to true the wheel. The "Pro" mandrel seemed to allow non-centered mounting. Even a good drill press is not perfectly centered. Some say you can do more damage then good.

So, my little test is not something others do?
I must admit that I do not believe that any successful racers that I know of use a test like that.

Improving wheels at home is tricky, to be sure. If you have a very good drill press with a low amount of radial runout (e.g. a proxxon), you might be able to rig up a poor man's lathing setup. There's also the Derbyworx Wheel Shaver, but that's an extremely fiddly device to use.

My advice: Buy a few extra tubes of wheels, build a FatSebastian runout gage and measure the wheels for concentricity. You should be able to find some between 2-3 thousandths out of round, and, if you're lucky, you might find a few "unicorns" with 1 thousandth or less. Of course, you should also spin test every wheel. A wheel that's concentric to the bore but wobbles all over the place is no good. I would say....if you're building one car, buy 3-4 extra tubes of wheels and measure the runout of all of them. Gather up all of the wheels of .003" runout or less, and, of these, pick the ones with the tightest bore and smoothest spin.

A set of pin gages from .095" to .098" can help you determine which wheels have the smallest bores.



Speedster
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Re: Wheel Test Question

Post by Speedster » Sat Apr 15, 2017 6:19 am

Derby Evolution sells a Concentricity gauge by Knotty Racing. It's listed under Speed Supplies. It sells for around $50.00.



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